1. Field of Invention
This invention relates to rotational molding of plastics and, in particular, to transfers useful to impart graphic and alphanumerical information to rotational molded products.
2. Brief Statement of the Prior Art
Rotational molding is traditionally used for fabrication of hollow form objects from plastics, particularly from polyethylene. Polyolefin surfaces, particularly polyethylene surfaces, however, resist acceptance of coats. A prevalent method of imparting coatings of materials such as printed matter or decoration has been to oxidize the polyethylene surface by flame treatment to improve adhesion of subsequently applied materials. A less destructive method is described in U.S. Pat. No. 4,352,762 in which decorative or alphanumerical indicia are applied as a viscous oil suspension to the interior mold surface by silk screen printing for transfer to the molded part during molding. Further developments of this approach have included transferring indicia from a carrier sheet by burnishing the indicia onto the interior surface of the mold; see U.S. Pat. No. 4,519,972. These developments spurned other developments such as disclosed in U.S. Pat. Nos. 5,648,030 and 5,498,307. Commercial practice with such graphics transfers developed a technique of spraying the interior surfaces of the mold with an adhesive to enhance bonding, and hence transfer, of the graphics indicia to the mold surfaces from a carrier sheet. In practice, however, the adhesives are often not applied uniformly and frequently are used in excess, causing product discoloration and adhesive buildup on the mold surfaces. The adhesive sprays also use volatile solvents which present environmental concerns during use, shipment and storage. If not completely expelled prior to application of the transfer, any residual solvent will damage the indicia of the transfer. The application of an adhesive to the mold surface prior to application of the transfer also adds a further step to the molding operation, prolonging the molding cycle time.